fixed mapping struct bytes copy

Source

// SPDX-License-Identifier: UNLICENSED
pragma solidity 0.8.35;

/* ===ARENA-MANIFEST===
{"deploy":{"contract":"C","args":[],"value":0},"entry":{"function":"run","args":[],"value":0},"lane":"S","feature":"fixed-mapping-struct-bytes-copy"}
===END-ARENA-MANIFEST=== */

struct Box {
    bytes data;
    mapping(uint256 => uint256) other;
}

contract C {
    Box[1] boxes;

    function run() external returns (uint256) {
        boxes[0].data = hex"1234";
        bytes memory copied = boxes[0].data;
        return copied.length * 100 + uint8(copied[1]);
    }
}